1. Field of the Invention
This disclosure relates to a system and method that provides an airborne vehicle operator environmental condition information to assist in operating the airborne vehicle in less than optimal visibility situations.
2. Background Art
Low or no visibility situations, sometimes called degraded usable cue environments (DUCE), can severely limit a pilot's<situational awareness (SA) during take-off and landing operations. The presence of obscurants such as dust, sand, snow, etc. beneath the aircraft limits the use of human visual imaging as a way to determine terrain features. Ensuring the utmost safety under these conditions requires a detailed real time terrain map indicating ground features such as rocks, boulders, ditches, fence posts, and telephone poles, etc. Existing systems, however, suffer from drawbacks that limit their use for producing such a real time terrain map.
Traditional radar based scanning systems are limited in resolution of terrain features as well as maximum scan angle capability. Radar sensors are also susceptible to specular reflections from several natural materials, which can further diminish the terrain resolution. Furthermore, at large scan angles, the main lobe of the radar signal widens resulting in a large RF footprint on the ground. This limits the ability of the aircraft to operate covertly.
Millimeter wave (MMW) scanning radar works on a similar principle as traditional radar systems. Due to its reduced wavelength (typically 77 GHz), MMW radars are capable of relatively high cross range resolution. This however comes at the expense of a large aperture size. As an example, a 1° conical footprint requires a 224 mm (9″) clear aperture. In general, both radar and MMW systems have size, weight, and power draw requirements that are not ideally suited for helicopter applications.
Another approach involves splitting optical signals into equal intensity sub-beams that are optically delayed via the use of plane-parallel plates. These individual sub-beams can be thought of as elements of a phased array. Beam steering is then achieved by wavelength tuning the primary laser source such that the relative phase of these sub-beams is varied in time. While this approach generates one-dimensional beam steering, the technique can be extended to two dimensions by placing a second set of parallel plates in series. However, this concept only works for well-defined phase differences between the individual beams in the array. Introduction of phase error can significantly reduce the on-axis optical power and degrade the resolution of the measurement. For this reason, this technique is not recommended for applications involving vibrating platforms.
Other work involves use of micro-electro-mechanical systems (MEMS) devices for beam steering applications. While considerable work has been done in this area towards improving the speed, scan angle, and intrinsic stability of MEMS devices, the insertion loss and power handling capability of such devices requires further improvement prior to use in high power LIDAR applications.
Other techniques such as acousto-optic beam deflectors have also been considered. Acousto-optic devices are fast, but suffer from low efficiency and produce an unwanted zero-order diffraction beam.
Existing techniques are not capable of meeting the size, weight, power draw, vibration, shock, update rate, and other essential harsh environmental requirements of a helicopter platform. More importantly, a viable technology must demonstrate reliable performance in a degraded visual environment (DyE).